HSC Physics Question Thread

[Dante1091]

Hello guys,
How do I do these questions
(from 2011 CSSA)

[bsdfjnlkasn]

Hello guys,
How do I do these questions
(from 2011 CSSA)

Hey there!

For Q12: I believe doubling the speed halves the period so the answer is A (thanks to the correction below ) as the EMF increases with increasing change of flux - the consequence of increased speed of rotation

Q13: Kiwiberry did some awesome working for a similar question here: https://atarnotes.com/forum/index.php?topic=164552.msg965221#msg965221 Hopefully the explanation helps as the method is exactly the same. This is a fairly common MC so now you'll nail it in your trial!

Q19: D
For this we need to remember that since Copper is a metal, it exists as a lattice. When energy is supplied, the particles begin to vibrate vigorously which increases the number of intermolecular collisions. This inhibits conductivity as it makes it harder for a clear flow of charge to be established i.e. resistance increases. Silicon is different because, being a semi-conductor, it's valence band and conduction bands are separated. Therefore, energy must be supplied in order for the electrons in the valence band to bridge the gap and so, the silicon to conduct. Energy in this case is supplied by heating the element which in turn increases conductivity as more charges are able to access the conduction band and move freely.  The following diagram might be familiar/helpful to distinguish between the specified conductor and semi-conductor:



Q16:
So after equating F_B and F_E, we deduce:
r=mv\qB (lol someone please correct this formatting)
Looking at all the variables, we know in order to increase r we have to increase the variables in the numerator. The only option this leaves us with is A

Hopefully this helped!

[blasonduo]

Hey there!

For Q12: I believe doubling the speed halves the period so the answer is C

Hello! Thanks for helping!

Just remember though, if something increases in speed, there is a larger change in flux, and thus more current can flow, So this will be A

[kiwiberry]

Hello guys,
How do I do these questions
(from 2011 CSSA)

In case you're still confused about Q13
The force that X exerts on Y is
Because X and Y are parallel, this force will be attractive, so to the left.
The current running through Z will be 4I₁, so the force Z exerts on Y is
Because Y and Z are antiparallel, this force will be repulsive and also be to the left
Therefore the total force on Y will be F+2F=3F N left!

[Dante1091]

Thank you guys!

[austv99]

Hi,
Confused with whether the radial magnetic field will allow for increased change in flux or none at all? So whether the current output increases or not?

Thanks.

[bsdfjnlkasn]

Hi,
Confused with whether the radial magnetic field will allow for increased change in flux or none at all? So whether the current output increases or not?

Thanks.

Hey there!

We use a radial magnetic field to maintain the maximum possible torque in a generator. It ensues that the armature/current carrying conductor is always parallel to the magnetic field. Considering torque is proportional to cos(theta) and that cos0=1, we know this arrangement of the magnetic field and coil will give a maximum torque.

*theta = 0 because the two are parallel, meaning the coil is not inclined to the field

That is the main reason we use a radial magnetic field.

I'm not so sure about the question you asked though. Despite the coil cutting flux lines when it is rotating, I don't know whether this will induce an EMF because the field strength of the radial magnetic field may be uniform..

[winstondarmawan]

Hello! Would like to check a few of these questions and help for others:
15. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/20677063_1291831764275677_1507629571_o.png?oh=918648afa568be439af7221113370957&oe=5988D33D Is this B?
19, 20. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20668365_1291831997608987_996377233_n.png?oh=f72244959b80493fa41debb899a2185f&oe=59889344 Are these C and B?
25. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20632754_1291832540942266_456187579_n.png?oh=71fb21ccdf5c1e3795d03945f8bd525b&oe=5988BBEE Distance goes on the x-axis right? Also need help with part b.
TIA

[blasonduo]

15) I do believe this is correct, this question is trying to trick you into thinking the magnets are super conductors! (If they were the magnetic field lines wouldn't pass through them!)

19) Yep! C is correct, A control is a very easy way to identify any uncontrolled variables.

20) This one is tricky! But in my opinion, I would go A. B doesn't really fit as placing no data because of a potential bias won't increase reliability. For an experiment, data is needed. Having peer-reviewed articles does increase reliability and does reduce this bias (and hence why I think A is better suited) as peer-reviewers are experts in the field, they know what they are talking about. Also, multiple peer-reviewers are present will increase this. Overall resulting in a more reliable report.

25) The general rule of thumb here is that the INDEPENDENT variable goes on x-axis, In this case, we aren't specifically told, but it can be safe to assume, that distance was the independent variable here For part b, I will quickly draw up the graph and do b for you shortly

[jakesilove]

15) I do believe this is correct, this question is trying to trick you into thinking the magnets are super conductors! (If they were the magnetic field lines wouldn't pass through them!)

19) Yep! C is correct, A control is a very easy way to identify any uncontrolled variables.

20) This one is tricky! But in my opinion, I would go A. B doesn't really fit as placing no data because of a potential bias won't increase reliability. For an experiment, data is needed. Having peer-reviewed articles does increase reliability and does reduce this bias (and hence why I think A is better suited) as peer-reviewers are experts in the field, they know what they are talking about. Also, multiple peer-reviewers are present will increase this. Overall resulting in a more reliable report.

25) The general rule of thumb here is that the INDEPENDENT variable goes on x-axis, In this case, we aren't specifically told, but it can be safe to assume, that distance was the independent variable here For part b, I will quickly draw up the graph and do b for you shortly

Absolutely legendary answer, thanks for all the incredible contributions!

[blasonduo]

Hmm... for the graph, it does show the relationship of distance to be inversely proportional to Force, I reckon it's trying to say, since the Forces are so minuscule, there is a large margin or error (the wind could change the values by quite a lot) and the experiment was only repeated 4 times. So due to this, more repetition is needed to identify if the recorded values are correct.

[austv99]

Hey,
Could someone explain both parts?

[kiwiberry]

Hey,
Could someone explain both parts?

Bohr proposed that electrons existed in discrete stationary states/energy levels, and that they would only absorb EMR when transitioning to a higher energy state and emit EMR when transitioning to a lower energy state. This would mean that only certain wavelengths of EMR would be emitted from electron transitions. The Balmer series showed that the emission spectrum of hydrogen was not a continuous rainbow but instead discrete lines at certain wavelengths - this lent support to Bohr's model.

The Balmer series shows the spectral lines that result from electron transitions from n>2 to n=2. So the four lines in the diagram show the transitions from n=3-->2, 4-->2, 5-->2 and 6-->2. The next line will be the transition from n=7-->2. We can find the wavelength of this line using Rydberg's equation with n_f=2 and n_i=7:
And then to find the energy of EMR with this wavelength, sub \(\lambda \) into \(E=\frac{hc}{\lambda }\).

Hope this helped

[mercurry]

Heyy, how do I answer these questions? I tried but I'm totally lost lol.

a) The currents are in opposite directions, therefore the forces experienced repel. (?? what's the best answer for two marks?)
b) ?? Something to do with weight?
c) yeahhh nah

Source: HSC 2005, Q21

[kiwiberry]

Heyy, how do I answer these questions? I tried but I'm totally lost lol.

a) The currents are in opposite directions, therefore the forces experienced repel. (?? what's the best answer for two marks?)
b) ?? Something to do with weight?
c) yeahhh nah

Source: HSC 2005, Q21

a) Yep Because the tubes carry current in opposite directions, they will exert a repulsive force on each other. However, because the bottom one is supported by the rack it can't move down, so only the top tube jumps up.

b) Yeah, for the top tube to jump up, the force due to the currents must be greater than its weight force.
So the minimum current will be just above 221.359 A

c) Because transmission lines are very long and carry high currents, they will need to be placed far apart to ensure the force between them is at a minimum.

Hope this helped!